阅读理解。
Each Tuesday afternoon, after the bell rings for the fourth period, Liu becomes a fashion designer. At the
same time, the rest of the students at the High School Attached to Yunnan Normal University in Kunming are
also having classes a little bit different from the usual ones. Some students dance, others create robots, and
still others review films. These are just a few of the other 27 elective (选修的) courses besides Liu's sewing
class that the school began to offer last month.
"The fashion design class has become the bright point of my week. I learn how to choose colors and
fabrics (织物) as well as sewing and sketching (素描) skills. It's all helping me to realize the dream of
becoming a fashion designer I've had since I was a little girl," Liu said.
Design is Liu's favorite, but for other students the electives are interesting lessons which relieve (舒缓)
the pressures of schoolwork. Some students, for example, are learning how to play bridge. Chen Xi, 15, is
one of them. She said, "Many people think that playing a card game like this in class is a waste of time. But
in fact, bridge is a very challenging game that helps develop memory and math skills."
1. How often do the students have elective classes? [ ]
A. Once a week
B. Once a month
C. Once a term
D. Once a year
2. How many elective courses had the school offered by last month? [ ]
A. 27
B. 28
C. 26
D. 25
3. Why did the students like to have elective classes?[ ]
A. Because the elective classes are easier.
B. Because they needn't do any homework in the elective classes.
C. Because they can get an opportunity to relieve their pressures.
D. Because they want to be fashion designers in the future.
4. According to the passage many people think _____ in class is a waste of time.[ ]
A. dancing
B. creating robots
C. playing a card game
D. reviewing films
MnCl2 + Cl2↑+ 2X根据上述已配平的化学方程式，可知X的化学式为（ ）